The present invention relates to an image display apparatus and, more particularly, to a portable head-mounted image display apparatus which can be retained on the user""s head or face.
Helmet- and goggle-type head-mounted image display apparatuses, which are designed to be retained on the user""s head or face, have heretofore been developed for the purpose of enabling the user to enjoy virtual reality or a wide-screen image by oneself.
Conventional head-mounted image display apparatuses, which are retained on the observer""s head to project a virtual image in the air for observation, include one type in which a virtual image of a two-dimensional image display device, e.g., a liquid crystal display device, is formed by a combination of an optical path splitting device, e.g., a half-mirror or a beam splitter, and a concave ocular mirror, as disclosed, for example, in Japanese Patent Application Laid-Open (KOKAI) No. 03-191389 (1991). This type of head-mounted image display apparatus will be explained below with reference to the sectional view of FIG. 18. A beam splitter surface 4 is disposed in front of an eyeball position (eye point) 2 of an observer 1 so as to diagonally intersect the observer""s visual axis 3. A concave ocular mirror 5 is disposed below the beam splitter surface 4 so as to extend substantially parallel to the visual axis 3, and a two-dimensional image display device 6 is disposed to face the concave ocular mirror 5 across the beam splitter surface 4. A reference axis 8 which intersects the visual axis 3 at right angles is disposed to extend through the display center 7 of the two-dimensional image display device 6 and also through the center of the concave ocular mirror 5. In this arrangement, light from the two-dimensional image display device 6 passes through the beam splitter surface 4 and is reflected by the concave ocular mirror 5 and then reflected by the beam splitter surface 4 to reach the eyeball position 2. Thus, a virtual image of the image displayed on the two-dimensional image display device 6 is formed in the air by the action of the concave ocular mirror 5, and the observer can view the displayed image. An outside, real world image can be viewed directly through the beam splitter surface 4.
The conventional head-mounted image display apparatus arranged as described above suffers, however, from the problem that the substrate of the two-dimensional image display device 6, e.g., a liquid crystal display device, is larger in size than the display screen thereof and hence interferes with the observer""s head.
The problem of the conventional head-mounted image display apparatus will be explained below more specifically. The two-dimensional image display device 6 needs to raise the pixel density in the display screen thereof and to thereby increase the number of pixels per unit area in order to realize high-definition display. Therefore, it is necessary to achieve electrical connection by leading electric wirings for switching of the pixels to the outside of the display screen. When the number of pixels is 100,000, for example, the number of electrical connections required is 300. Therefore, the conventional practice is to fabricate, a switching circuit at the periphery of the display screen to thereby reduce the number of electrical connections, i.e., to ten-odd connections. For the above-described reason, the substrate of the two-dimensional display device needs an area for electrical connection of the pixels with switching elements in addition to the area for display and requires a substrate larger in size than the display screen.
Thus, the half-mirror or beam splitter surface 4 must be disposed at a predetermined distance from the observer""s eye 2 in order to prevent the substrate of the two-dimensional image display device 6 from interfering with the observer""s head. Accordingly, when it is intended to widen the field angle for observation, the size of the half-mirror or beam splitter surface 4 increases, resulting in an increase in the overall size of the apparatus. In the case of a head-mounted image display apparatus such as that shown in FIG. 18, the increase of the size and weight is a principal factor in making the user feel uncomfortable when wearing the display apparatus, which is a serious problem.
In view of the above-described problems of the background art, it is an object of the present invention to provide a head-mounted image display apparatus which is designed so that the field angle for observation can be widened without causing the substrate of a two-dimensional image display device to interfere with the observer""s head and without increasing the overall size of the apparatus.
To attain the above-described object, the present invention first provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis passing through the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is reflected by the semitransparent reflecting surface is defined as a visual axis, and the semitransparent reflecting surface is disposed at a tilt to the image axis to change the angle of inclination of the semitransparent reflecting surface to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Secondly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis passing through the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is reflected by the semitransparent reflecting surface is defined as a visual axis, and the magnifying reflecting mirror is disposed at a tilt to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Thirdly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis passing through the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is reflected by the semitransparent reflecting surface is defined as a visual axis, and the magnifying reflecting mirror is shifted with respect to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Fourthly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, the semitransparent reflecting surface is a partially transmitting-reflecting surface composed of transmitting and reflecting regions which are locally distinguished from each other, and a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is transmitted by the partially transmitting-reflecting surface is defined as a visual axis. The partially transmitting-reflecting surface is disposed at a tilt to the image axis to change the angle of inclination of the partially transmitting-reflecting surface to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Fifthly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, the magnifying reflecting mirror is a partially transmitting-reflecting surface composed of transmitting and reflecting regions which are locally distinguished from each other, and a straight line that connects an eye point and a position where the optical axis reflected by the partially transmitting-reflecting surface is transmitted by the semitransparent reflecting surface is defined as a visual axis. The partially transmitting-reflecting surface is disposed at a tilt to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Sixthly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is transmitted by the semitransparent reflecting surface is defined as a visual axis, and the magnifying reflecting mirror is shifted with respect to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Seventhly, the present invention provides a face-mounted image display apparatus including a face-mounted unit which has an image display device with a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis leaving the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path, and a support member for retaining the face-mounted unit on the observer""s head. In the image display apparatus, a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is tangent to the semitransparent reflecting surface is defined as a visual axis, and at least the semitransparent reflecting surface or the magnifying reflecting mirror is decentered so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Eighthly, the present invention provides a head-mounted image display apparatus having an image display device, a semitransparent reflecting mirror, and a magnifying reflecting mirror, in which the image display device is used as an object point of the magnifying reflecting mirror, and the object point is projected in the air as an enlarged image for the observer without effecting image formation in the optical path. In the image display apparatus, either or both the semitransparent reflecting mirror and the magnifying reflecting mirror are decentered so that the display center of the image display device can be shifted away from the observer""s head with respect to a reference axis which perpendicularly intersects the observer""s visual axis lying when he or she sees forward.
In the first to seventh image display apparatuses of the present invention, the semitransparent reflecting surface may be formed from a half-mirror or a prism.
It is preferable that the angle made between the line normal to the semitransparent reflecting surface and the image axis should be smaller than xcfx80/4.
When the semitransparent reflecting surface is formed from a half-mirror, the angle xcex8 between the line normal to the half-mirror and the image axis preferably satisfies the following condition:
xcfx80/4xe2x88x92xcfx89/2xe2x89xa6xcex8 less than xcfx80/4 
where xcfx89 is a half of the vertical field angle.
When the semitransparent reflecting surface is formed from a prism beam splitter having a half-mirror surface, the angle xcex8 between the line normal to the half-mirror surface and the image axis preferably satisfies the following condition:
xcfx80/4xe2x88x92xcfx86/2xe2x89xa6xcex8 less than xcfx80/4 
where xcfx89xe2x80x2=sinxe2x88x921 (sinxcfx86/n), xcfx89 is a half of the vertical field angle, and n is the refractive index of a medium constituting the prism.
In the fourth and fifth image display apparatuses, the partially transmitting-reflecting surface may be a surface formed by partially coating aluminum on a surface of an optical member having a refractive index (n) larger than 1 (n greater than 1).
Ninthly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, the semitransparent reflecting surface is formed from a semitransparent film coated on a surface of an optical member having a refractive index (n) larger than 1 (n greater than 1), and a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting mirror is transmitted by the semitransparent reflecting surface is defined as a visual axis. The semitransparent reflecting surface is disposed at a tilt to the image axis to change the angle of inclination of the semitransparent reflecting surface to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
Tenthly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, the magnifying reflecting mirror is a magnifying reflecting surface formed from a semitransparent film coated on a surface of an optical member having a refractive index (n) larger than 1 (n greater than 1), and a straight line that connects an eye point and a position where the optical axis reflected by the magnifying reflecting surface is transmitted by the semitransparent reflecting surface is defined as a visual axis. The magnifying reflecting surface is disposed at a tilt to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
In the ninth and tenth image display apparatuses, the semitransparent film may be formed from a metallic thin film, a dielectric multilayer film, or a polarized beam splitter that distinguishes p-polarized light and s-polarized light by reflection and transmission, or transmission and reflection.
Eleventhly, the present invention provides an image display apparatus including an image display device having a screen for displaying an image, a semitransparent reflecting surface disposed at an angle of inclination to an optical axis which is determined by a bundle of rays emitted from the display screen, the optical axis being defined as an image axis, and a magnifying reflecting mirror disposed so that an optical axis reflected by the semitransparent reflecting surface goes to and returns from the magnifying reflecting mirror to form a turn-back optical path. In the image display apparatus, the magnifying reflecting mirror is a totally reflecting mirror, and a straight line that connects an eye point and a position where the optical axis reflected by the totally reflecting mirror is transmitted by the semitransparent reflecting surface is defined as a visual axis. The totally reflecting mirror is disposed at a tilt to the image axis so that the angle (xcfx86) made by intersection of the image axis extending from the image display device and the visual axis extending from the eye point is larger than 90xc2x0 (xcfx86 greater than 90xc2x0).
In the first to eleventh image display apparatuses of the present invention, either or both the optical path splitting device and the concave ocular mirror are decentered with respect to a reference axis perpendicularly intersecting the observer""s visual axis lying when he or she sees forward. Accordingly, the display center of the two-dimensional display device can be shifted away from the observer""s head, so that the two-dimensional display device will not interfere with the observer""s head. It is therefore possible to widen the field angle for observation without increasing the overall size of the apparatus.
In addition, when the angle made between the line normal to the half-mirror or half-mirror surface and the optical axis of the image display device is set so as to be smaller than xcfx80/4, it is possible to reduce the area of the half-mirror or the volume of the prism beam splitter. In addition, the distance between the projection optical system and the image display device shortens, so that the diopter adjustable range enlarges. Further, the distance (working distance) between the projection optical system and the observer""s eye lengthens. Accordingly, the user can observe a displayed image with his/her spectacles on.
Still other objects and advantages of the invention will in part by obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.